1. Field of the Invention
The present invention is related to catalytic converters for catalytically reacting with exhaust gas of internal combustion engines, and more particularly to a warm-up catalytic converter for use during initial engine operation. Still more particularly, the present invention is related to a catalytic converter having an axial flow mode and a radial flow mode and a valve for selectively switching exhaust gas flow from the radial flow mode to the axial flow mode, wherein catalytic reaction of exhaust gas occurs during the radial flow mode.
2. Description of the Related Art
Because harmful pollutants are contained in the exhaust gas of internal combustion engines, such as carbon monoxide, nitrous oxides and unburned hydrocarbons, catalytic converters are widely used to catalytically react with the exhaust gas to thereby greatly reduce pollutant emissions. Problematically, however, the noble metal catalyst of the catalytic converter must be raised to a minimum operational temperature, the "light-off" temperature, in order for the exhaust gas pollutants to be catalytically reacted at maximum efficiency.
In vehicular applications, the catalytic converter is usually located relatively far downstream of the engine under the vehicle floor. Accordingly, when the engine is cold started and the exhaust gas is relatively cool, the catalytic converter will operate at reduced efficiency until the exhaust gas becomes hot enough for the catalyst to achieve its light-off temperature. During this time of initial engine operation, considerable pollutant output can occur.
In order to raise the catalytic converter to its light-off temperature as quickly as possible, supplemental heat systems can be utilized. Supplemental heat systems generally are of two types, electrical and gas fired. Electrical type supplemental heat systems require a large current for providing sufficient heat which tends to tax the electrical system of the vehicle, and there is a potential problem associated with shorting of the electrical path due to insulator failure. Gas fired type supplemental heat systems require an auxiliary burner unit interfaced with the exhaust system upstream of the catalytic converter, and the dual goals of efficient operation and minimal mechanical complexity are difficult to achieve in practice.
Accordingly, it would be beneficial if a warm-up catalytic converter could be provided immediately adjacent to the exhaust manifold which would efficiently operate during the initial period of engine operation and wherein the operation thereof would be selectively controllable.